Formation of PVP/nimesulide microspheres by supercritical antisolvent coprecipitation

In order to improve the bioavailability of poorly water soluble drugs, an effective technique is the coprecipitation of the drug with a hydrophilic polymer. In this work, the coprecipitation of polyvinylpyrrolidone/nimesulide (PVP/NIM) nanostructured microparticles using Supercritical Antisolvent (SAS) was proposed. The effects of the main process parameters, such as polymer/drug ratio, overall concentration, operating pressure and temperature were investigated to identify successful operating conditions for SAS coprecipitation. Microparticles with a mean diameter ranging between 1.7 and 4 μm (calculated in number of particles) were successfully produced; they were characterized using different analytical techniques, to demonstrate the occurred coprecipitation. Precipitation yield was found to be about 100% with respect to the amount of solute dissolved in the starting solution. Drug release analyses revealed that Nimesulide dissolution rate from PVP/NIM microparticles in a phosphate buffered saline solution (PBS) was 2.5 times faster with respect to unprocessed drug. The possible precipitation mechanisms involved in the process were discussed.